Magnetron sputtering is a well known process for applying thin coatings onto objects. Sputtering is implemented by creating an electrical plasma over the surface of an target emitter material in a low-pressure gas atmosphere. Gas ions from the plasma are accelerated by electrical fields to bombard and thereby eject atoms from the surface of the emitter. These atoms travel through the gas environment until they impact the surface of the object to be coated, where they bond to the object, creating the coating layer.
A standard method of improving the efficiency of sputtering has been to use magnetic fields to confine electrons to the glow region in the vicinity of the emitter surface. The addition of such magnetic fields increases the rate of ionization which in turn increases the ion energy and the number of ions in the plasma. The increased ion energy and number of ions increases the overall sputtering rate.
Cylindrical magnetron sputtering devices are known which utilize elongated emitters and solenoid coils which produce flux lines parallel to the axis of the emitter. A significant drawback to such cylindrical sputtering devices is that they suffer from undesirable end effects. In a cylindrical magnetron, the direction of the electron drift velocity vector causes the electrons to orbit around the longitudinal axis of the emitter. However, the electrons tend to leak out or escape their orbits near each end of the emitter, resulting in lower ionization intensities and therefore lower sputtering rates at each end of the emitter. As a result, the portions of the object to be coated in the vicinity of the ends of the emitter may receive little or no coating.
Another drawback to cylindrical magnetrons is that in order to uniformly coat long objects such as pipes, a corresponding long vacuum chamber, emitter and solenoid coil must be provided, adding to the complexity and expense of the apparatus.
Therefore, there is a need in the art for apparatuses and methods suitable for uniformly coating long cylindrical objects such as pipes and the like.